Control Authority of a Projectile Equipped With an Internal Unbalanced Part

Report No. ARL-CR-555
Authors: Geoffrey W. Frost and Mark F. Costello
Date/Pages: November 2004; 60 pages
Abstract: A key technical challenge for smart weapon developers is design of appropriate control mechanisms that provide sufficient control authority to enable correction of typical trajectory errors while not excessively burdening the overall weapon design. The work reported here considers a rotating mass unbalance control mechanism created by radial orientation of an internal part. To investigate the potential of this control mechanism, a seven degree-of-freedom flight dynamic model of a projectile equipped with an internal part is defined. Using this dynamic model, it is shown that by holding the internal part fixed with respect to a nonrolling reference frame, predictable trajectory changes are generated, including predictable impact point changes. As expected, when unbalance-offset distance or mass is increased, control authority increases proportionally. This control mechanism is capable of creating impact point changes that are the same order of magnitude as dispersion caused by errors induced at launch and in flight. To achieve this level of control authority, the projectile must be designed less stable than is typical of conventional uncontrolled fin and spin-stabilized projectiles.
Distribution: Approved for public release
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Last Update / Reviewed: November 1, 2004